The present invention relates to an apparatus for detecting the leakage of liquid sodium and, more particularly, to such an apparatus capable of the presence of detecting leakage as a change in electrical leak current. Still more particularly, the invention relates to an apparatus for rapidly detecting the leakage of coolant in a sodium-cooled nuclear reactor.
Because of low vapour pressure, an excellent performance as a heat transfer medium, good stability against radioactive rays and of particularly small slowing-down power, liquid sodium is popularly used in fast breeder reactors and systems associated therewith. In such facilities, it is necessary to detect the leakage of the liquid sodium from essential parts promptly and securely, which demands the development of a detecting apparatus of moderate cost.
Conventionally, there are typically employed three methods for detecting the leakage of liquid sodium.
The first known method is to use the so-called electrode type detector consisting of a ceramic-insulated tube accomodating a metal wire, while the second known method utilizes a smoke detector sensitive to the smoke of sodium oxide which results from the leakage, and the third known method is to utilize a hydrogen detector sensitive to hydrogen gas which is produced as a resultant of the reaction of the sodium and atmospheric water vapour.
These known measures have been found, however, to be inconvenient or unsatisfactory for the reasons discussed below. Namely, the first method is not capable of immediate detection of the leak, because the elctrode-type detector is sensitive only to a relatively large quantity of sodium leakage, and also is likely to respond to electrically conductive substances other than sodium. In addition, the detector of this type cannot be placed at any desired location due to the structure thereof. In the second method described above, the detector tends to by erroneously operated or actuated by smoke from sources other than sodium oxide. The smoke detector is often invalid because only a part of the leaked sodium passes through the heat insulator surrounding the leaking point to the atmosphere to generate the smoke. The third method requires an expensive detector and thus is not practical when a large number of detectors in numerous places is necessary.